The present invention relates to improvements in or relating to methods and apparatus for introducing elongate members into the ground.
A known type of energy system which makes use of ground heat uses ground loops which extend down into the ground from a building to be heated or cooled. Each ground loop consists of a relatively narrow pipe through which a heat conducting fluid can pass down into the ground in liquid form, and a relatively wide pipe through which the fluid may return to the surface, having gained or discharged heat from or to the ground. This energy is extracted at the surface by a heat exchanger. The two pipes of the ground loop typically extend alongside each other into the ground and form an elongate member which is only a few centimeters in width. In many circumstances, introduction of the ground loop into the ground cannot be achieved by means of a simple drill arrangement to form a bore, because the small size of the required bore, and the depth required, create a significant risk of the bore collapsing as the drill retreats. Accordingly, it is common to use two drilling operations. In a first, a wide pipe with cutting teeth around its lowermost mouth is drilled into the ground by rotation, until bedrock is reached, thus providing a lining through which a second drill can reach down to bore into the bedrock, with the bore being prevented from collapse by the lining. This has the disadvantage of requiring two drilling operations.
In an alternative, a pipe is used to drive a drill head which is lost as the pipe is removed, or has a mechanical gate which opens as the pipe and head are removed, in either event allowing the ground loop to be left in the bore. Lost cutting heads represent an unacceptable cost. Mechanical release mechanisms and mechanical gates and other arrangements are prone to failure, which may result in the bore being unusable, and a further bore being required.